Today’s Catechism sections discuss merit. Supporting material comes from the “Summa Theologica”.

III. Merit

You are glorified in the assembly of your Holy Ones, for in crowning their merits you are crowning your own gifts.59

2006 The term "merit" refers in general to the recompense owed by a community or a society for the action of one of its members, experienced either as beneficial or harmful, deserving reward or punishment. Merit is relative to the virtue of justice, in conformity with the principle of equality which governs it.

2007 With regard to God, there is no strict right to any merit on the part of man. Between God and us there is an immeasurable inequality, for we have received everything from him, our Creator.

2008 The merit of man before God in the Christian life arises from the fact that God has freely chosen to associate man with the work of his grace. The fatherly action of God is first on his own initiative, and then follows man's free acting through his collaboration, so that the merit of good works is to be attributed in the first place to the grace of God, then to the faithful. Man's merit, moreover, itself is due to God, for his good actions proceed in Christ, from the predispositions and assistance given by the Holy Spirit.

2009 Filial adoption, in making us partakers by grace in the divine nature, can bestow true merit on us as a result of God's gratuitous justice. This is our right by grace, the full right of love, making us "co-heirs" with Christ and worthy of obtaining "the promised inheritance of eternal life."60 The merits of our good works are gifts of the divine goodness.61 "Grace has gone before us; now we are given what is due.... Our merits are God's gifts."62

2010 Since the initiative belongs to God in the order of grace, no one can merit the initial grace of forgiveness and justification, at the beginning of conversion. Moved by the Holy Spirit and by charity, we can then merit for ourselves and for others the graces needed for our sanctification, for the increase of grace and charity, and for the attainment of eternal life. Even temporal goods like health and friendship can be merited in accordance with God's wisdom. These graces and goods are the object of Christian prayer. Prayer attends to the grace we need for meritorious actions.

2011 The charity of Christ is the source in us of all our merits before God. Grace, by uniting us to Christ in active love, ensures the supernatural quality of our acts and consequently their merit before God and before men. The saints have always had a lively awareness that their merits were pure grace.

After earth's exile, I hope to go and enjoy you in the fatherland, but I do not want to lay up merits for heaven. I want to work for your love alone.... In the evening of this life, I shall appear before you with empty hands, for I do not ask you, Lord, to count my works. All our justice is blemished in your eyes. I wish, then, to be clothed in your own justice and to receive from your love the eternal possession of yourself.63

IN BRIEF

2025 We can have merit in God's sight only because of God's free plan to associate man with the work of his grace. Merit is to be ascribed in the first place to the grace of God, and secondly to man's collaboration. Man's merit is due to God.

2026 The grace of the Holy Spirit can confer true merit on us, by virtue of our adoptive filiation, and in accordance with God's gratuitous justice. Charity is the principal source of merit in us before God.

2027 No one can merit the initial grace which is at the origin of conversion. Moved by the Holy Spirit, we can merit for ourselves and for others all the graces needed to attain eternal life, as well as necessary temporal goods.

In the “Summa Theologica” (Prima Secundæ Partis, 114, 1), St. Thomas Aquinas discusses merit.

Article 1. Whether a man may merit anything from God?

Objection 1. It would seem that a man can merit nothing from God. For no one, it would seem, merits by giving another his due. But by all the good we do, we cannot make sufficient return to God, since yet more is His due, as also the Philosopher says (Ethic. viii, 14). Hence it is written (Luke 17:10): "When you have done all these things that are commanded you, say: We are unprofitable servants; we have done that which we ought to do." Therefore a man can merit nothing from God.

Objection 2. Further, it would seem that a man merits nothing from God, by what profits himself only, and profits God nothing. Now by acting well, a man profits himself or another man, but not God, for it is written (Job 35:7): "If thou do justly, what shalt thou give Him, or what shall He receive of thy hand." Hence a man can merit nothing from God.

Objection 3. Further, whoever merits anything from another makes him his debtor; for a man's wage is a debt due to him. Now God is no one's debtor; hence it is written (Romans 11:35): "Who hath first given to Him, and recompense shall be made to him?" Hence no one can merit anything from God.

On the contrary, It is written (Jeremiah 31:16): "There is a reward for thy work." Now a reward means something bestowed by reason of merit. Hence it would seem that a man may merit from God.

I answer that, Merit and reward refer to the same, for a reward means something given anyone in return for work or toil, as a price for it. Hence, as it is an act of justice to give a just price for anything received from another, so also is it an act of justice to make a return for work or toil. Now justice is a kind of equality, as is clear from the Philosopher (Ethic. v, 3), and hence justice is simply between those that are simply equal; but where there is no absolute equality between them, neither is there absolute justice, but there may be a certain manner of justice, as when we speak of a father's or a master's right (Ethic. v, 6), as the Philosopher says. And hence where there is justice simply, there is the character of merit and reward simply. But where there is no simple right, but only relative, there is no character of merit simply, but only relatively, in so far as the character of justice is found there, since the child merits something from his father and the slave from his lord.

Now it is clear that between God and man there is the greatest inequality: for they are infinitely apart, and all man's good is from God. Hence there can be no justice of absolute equality between man and God, but only of a certain proportion, inasmuch as both operate after their own manner. Now the manner and measure of human virtue is in man from God. Hence man's merit with God only exists on the presupposition of the Divine ordination, so that man obtains from God, as a reward of his operation, what God gave him the power of operation for, even as natural things by their proper movements and operations obtain that to which they were ordained by God; differently, indeed, since the rational creature moves itself to act by its free-will, hence its action has the character of merit, which is not so in other creatures.

Reply to Objection 1. Man merits, inasmuch as he does what he ought, by his free-will; otherwise the act of justice whereby anyone discharges a debt would not be meritorious.

Reply to Objection 2. God seeks from our goods not profit, but glory, i.e. the manifestation of His goodness; even as He seeks it also in His own works. Now nothing accrues to Him, but only to ourselves, by our worship of Him. Hence we merit from God, not that by our works anything accrues to Him, but inasmuch as we work for His glory.

Reply to Objection 3. Since our action has the character of merit, only on the presupposition of the Divine ordination, it does not follow that God is made our debtor simply, but His own, inasmuch as it is right that His will should be carried out.

Footnotes

59 Roman Missal, Prefatio I de sanctis; Qui in Sanctorum concilio celebraris, et eorum coronando merita tua dona coronas, citing the "Doctor of grace," St. Augustine, En. in Ps. 102, 7: PL 37, 1321-1322.
60 Council of Trent (1547): DS 1546.
61 Cf. Council of Trent (1547): DS 1548.
62 St. Augustine, Sermo 298, 4-5: PL 38, 1367.
63 St. Therese of Lisieux, "Act of Offering" in Story of a Soul, tr. John Clarke (Washington Dc: ICS, 1981), 277.